Interaction of sulphur compounds with palladium

Abstract

The interaction of SO2, CS2 and H2S with evaporated films of Pd has been investigated in the temperature range from –80°C to about 250°C. At –80°C, rapid adsorption of SO2 and CS2 occurred but the initial uptake of both gases on the metal is probably dissociative and some incorporation also occurred. About 20 % of the total SO2 or CS2 adsorption at –80°C was reversible. No clear evidence was obtained for further incorporation of the two gases in Pd at temperatures up to 250°C. Extensive adsorption of H2 took place at –80°C on a Pd film which had been saturated with either SO2 or CS2. The chemisorption of H2S on Pd at –80°C occurred instantaneously but no hydrogen desorption was observed even on warming the film to 50°C. The completion of the surface layer at 25°C was followed by the formation of bulk sulphide. Above 70°C was more hydrogen was evolved than H2S adsorbed. Activation energies for the incorporation process were determined from the rates of H2S adsorption as the thickness of the sulphide layer increased over the temperature range 25-250°C. The condensation coefficient increased as the converage increased and this variation was interpreted in terms of a gradual transition from immobile to mobile adsorption during sulphidation. The slow step of the H2S reaction with Pd is considered to be dissociation at the sulphide interface.